*{
    margin: 0;
    padding: 0;

}
body{
    /*100%窗口高度*/
     height: 100vh; 
    /*弹性布局 水平+垂直居中*/
     display: flex;
    justify-content: center;
    align-items: center; 
 } 
  /* 搜索按钮 */
  .search_btn{
      /* 相对定位 */
    position: relative;
    z-index: 1;
    width: 60px;
    height: 60px;
    line-height: 60px; 
    text-align: center;
    /* 鼠标移入变小鼠标 */
    cursor:pointer;
    
 }  
 .search_btn .fa{
     color:#fff;
     font-size:22px;
 }
 /* 关闭按钮 */
 .close_btn{
     /* 绝对定位 */
    position: absolute;
    top:25px;
    right: 25px;
    z-index: 1;
    font-size: 25px;
    color:#fff;
    cursor:pointer;
    display: none;
} 
.container{
    position: fixed;
    width: 100%;
    height: 100%; 
    display: flex;
    justify-content: center;
    align-items: center; 
    /* 渐变元素 */
    background: linear-gradient(200deg,#6e86ee,#453c90);
    /* 将元素剪切为一个圆形（30px表示圆的半径，50%50%表示圆心的位置） */
     clip-path:circle(30px at 50% 50%);  
     /* 设置过渡 */
     transition: 0.4s;
}
.search_box{
    /* 默认宽度为0（隐藏） */
    width: 0;
    height: 50px;
    display: flex;
    border-bottom: 3px solid #fff;
    /* 溢出隐藏 */
    overflow: hidden;
    /* 设置过渡 */
    transition:0.3s;
}  
.search_box input{
    width: 100%;
    height: 100%;
    border: none;
    outline:none;
    background: none;
    color: #fff;
    font-size: 22px;
    text-indent: 8px;
}
.search_box input::placeholder{
    color:rgba(255,255,255, 0.7);
}
.search_box .fa{
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    color:#fff;
    font-size:22px;
    cursor:pointer;
} 
#search_btn:checked ~ .search_btn{
    display: none;

}
#search_btn:checked ~ .close_btn{
    display: block;
}
#search_btn:checked ~ .container{
    clip-path:circle(100%);
}
#search_btn:checked ~ .container .search_box{
    width: 400px;

} 